Sanding machine having means for preventing belt creeping



O 1957 I R. F. PENDE'RGAST 2,813,332

SANDING MACHINE HAVING MEANS FOR PREVENTING BELT CREEPING Filed Jan. 14, 1955 2 Sheets-Sheet 1 5 INVENTOR.

9 1: Lf Eva??? W6 19, 1957 R. F. PENDERGAST 2,313,382

SANDING MACHINE HAVING MEANS FOR PREVENTING BELT CREEPING 2 Sheets-Sheet 2 Filed Jan. 14, 1955 United States Patent SANDING MACHINE HAVING MEANS FOR PREVENTING BELT CREEPING Raymond F. Pendergast, Robinsdale, Minn. Application January 14, 1955, s ria N .4s1,sos Claims. (Cl. 51-435 there appears a pair of frame members and 12 which support at their upper ends a shaft 14 carrying a contact roll 16. The shaft 14 is the power shaft and is driven by means not shown. Mounted on the frame members 11 and 13 is an idler shaft 18 which carries a slightly smaller drum 20. The frame members 11 and 13 hang from a member not shown which carries both frame 10 and 12 and 11 and 13 in such a manner as to allow the belt to he slipped over the contact roll 16 and the idler drum 20. The face of the roll 16 is encased in a rubber sleeve .21 whose outer surface carries wales 22 spaced by grooves 24, which grooves are about one-half to twothirds the width of the wales. The surfaces of the wales are flat, that is, they all lie in a common cylindrical surface and the surfaces of the wales constitute from 50 to 70 percent of the total surface of the rubber sleeve. The wales are straight and are at an angle of 45 degrees with a plane at right angles to the axis of the drum 16.

Entrained over the drums 16 and is a belt 25 which is formed from a strip of sandpaper that has been spliced along the line 28. For purposes of definition, the flight bearing the numeral 26 in Figure 2 is called the departure flight, and the flight bearing the numeral 51is called the approach flight. While the line bearing the numeral 52 is the far side of the belt, it also indicates the uninterrupted path of the belt which is called the approach flight path. Usually, and for applicants sleeve, desirably, the sandpaper is as defined, namely, it has a paper backing. The thickness of the paper backing may vary with the coarseness of the grid carried by glue or other adhesive on the abrasive surface. In general, the stiffness of the paper does not contribute as much to the stiffness of the belt as does the hardened glue which holds the grit to the paper. There are some sanding belts made of woven materials, i. e., cotton, but which have little body. These belts do not function on applicants apparatus as Well as those having the paper backing, as will be explained hereinafter. I

Mounted above the roll 16 is a feed roll shaft 30 carrying a plurality of rubber-surfaced feed rollers 32. This shaft 30 is driven at a selected speed in the direction of the arrow 34, see Figure 2. The shaft 14 and the roll 16 are turning in the direction of the arrow 36. In a sanding operation, a piece of wood 38 (or other material including metal) is fed into the bight of the feed roll 32 and the roll 16. That is, the workpiece is advanced by the rolls 32 against the sanding surface of the belt 26.

The mounting of the idler shaft 18 is not shown in detail, but it .is standard. By manual means, :theshaft feet per minute.

Patented Nov. 19, 1957 18 can be raised at one end and lowered at the other, or vice versa, so as to increase the tightness of the belt at one side over its tightness on the other side. In belt operation, the belt always travels toward the high point. With the apparatus as thus described, the belt 26 may be caused to ride on center when not under load.

With the application of the load, such as workpiece 38, or with an uneven splice, the balance of the system is upset, and the belt will tend to crawl laterally either to the right or to the left as viewed in Figure 1. The rate of crawling may be very high. The belt may move from center against the operating machinery to the right or the left and destroy itself within a few seconds. This crawling is aided by the deep grooves 24 between the wales 22 on the rubber sleeve 21. These rubber sleeves have greatly changed woodworking practices because opcraters can lower the shaft 30 and exert such pressure on the piece that on one pass, one-sixteenth of an inch of wood can be removed, without tearing the sanding surface. Applicant is the first to utilize this rubber sleeve in a machine employing a wide and short sanding belt and operating at speeds between 3,000 and 6,000 linear The machine illustrated in Figure l is the only belt sander having a rubber sleeve on the contact roll which is on the market today. It will make a much deeper cut than will the drum around which sand paper is drawn.

The major object of this invention, therefore, is to prevent the belt 26 from moving laterally ofii the roll in either direction without further adjustment of the idler shaft 18 and irrespective of load. All attempts to utilize existing belt conveyor centering devices are valueless. These are devices in which pulleys engage the edge such as 40 of the belt 26, see Figure l, and by yielding to the pressure from the edge, cause a change in a shaft such as the idler shaft 18. Not only will the paper or heavy cloth edge 40 tray or crumble, but strains are placed upon the seam 28 which cause it to open. As stated, the destruction of the belt may be a matter of seconds. The R. P. M. of the shaft 14 is 1000, and this gives a linear speed on the belt of feet per second.

Applicants method is based upon lengthening the path of a substantial portion of the belt along one edge and doing this at a point close to the contact roll. Referring to Figure 1, consider that part of the belt between the dotted line 42 and the edge 40 as an edge strake 41. Applicant lengthens the path of the entire strake at a series of points such as along the dot-dash line 44 which is substantially parallel to the axis of the shaft 14. When the requisite pressure is applied, the belt stops creeping t0 the right. This seems to be in direct conflict with the long established principle that the belt moves toward the high point.

These and such other objects as may hereinafter appear are attained by the embodiment of the invention shown in the accompanying drawings, wherein:

Figure 1 is a front schematic elevation of the working parts of applicants sanding machine;

Figure 2 is a side elevation taken on the lines 2--.2 of Figure 1;

Figure 3 is a View taken on the line 3-3 of Figure 2;

Figure 4 is a schematic front elevation showing in exaggerated form how the belt creeps under the action of the work;

Figure 5 is a schematic front elevation showing in exaggerated form how the pulley re-directs the belt.

Continuing to refer to the drawings, particularly Figures l and 2, mounted by any suitable means on the frame member 10 at a point close to the contact roll 16 is a journal 46 (see Figure 3) in which is rotatably mounted a pin 48 upon which is pivoted an. arm 50 of a U-shaped member 51. The axis of the pin 48, referring to Figure 1, is at right angles to the axis of the shaft 14 and is parallel to a line connecting the centers of the shafts 14 and 18. This right angle relationship to ,the axis of the shaft 14 in parallel relationship to a line ;conne cting the axes of the shafts 14 and 18 is important, but a variation from the perfect position by or 15 degrees in certain directions is not too critical. What is important is that the pulley, shortly to be described, should entrain the belt without excessive slippage.

Referring to Figure 2, the normal flight of the belt, i. e., the approach flight path, is indicated by the line 52. See this numeral also in Figure 3. This last figure shows the axis of the pin 48 located one inch inside the plane containing the outside edge of the drum 16. The arm 50 mounted on the pin 48 is U-shaped and its second leg 53 carries rotatably a pulley 54. This pulley is seven inches long and the radius 56 which intersects the axis 57 of the pulley at right angles does so at a point 58 which is two inches from the outer end of the pulley.

The pulley is three inches in diameter. The position of the flight of the belt when not touched by the pulley is indicated by the cross section 60. The roll 16 is 25 inches wide and the belt in this case is 19 inches wide. The angle of the axis of the pulley 54 to the approach flight path 52 is about 30 degrees because a stop prevents further counter-clockwise movement of the U-shaped member 50. When the belt 26 commences to move to the right, it engages the roller 54 which is in the position 62 and climbs up its surface as indicated by the dash line 64. As the belt climbs the surface of the roller 54, it tends to rotate the U-shaped member 51 in a clockwise direction. Applicant has shown the belt as having climbed a considerable distance on the pulley, forming a sharp valley at the point 68. This is not exactly what happens.

Actually, the pulley mounted on the arm 50 commences to rotate clockwise around the pin 48 very slowly shortly after the belt engages the pulley. When the edge 40 of the belt reaches the point indicated by the numeral 40 in Figure 3, there is suificient pressure on the entire pulley and U-shaped member assembly to throw it into the solidline position shown in Figure 3. This does not occur gradually. When the critical point is reached, the pulley assembly moves into the solid line position and in so doing what applicant has referred to as the strake 41 is suddenly supported throughout its width by the pulley. In reaching this position, it will be noted that the edge 40 of the belt which is quite close to the edge 70 of the pulley slips away from the edge as the pulley moves into the solid-line position. The surface of the pulley is made of steel and its surface is smooth.

When the belt reaches the position shown in Figure 3, it ceases to creep to the right. Several theories may explain this. Applicants theory is, referring to Figures 1 and 2, that the work, moving against the direction of movement of the belt, tends to push the belt to one side or the other depending on the straightness of the belt or upon the angle of the work as it enters the bight between the pulleys 32 and the belt and depending upon the direction of the wales 22 on the rubber sleeve. The result is the the belt moves toward that side of the assembly toward which its grains push it. This is possible because of the comparatively long flight between the takeoff line 72, referring to Figure 4, where the belt leaves the idler roller 20, and the landing line 74 where it contacts the drive roller. The distance is such that the paper of the belt can be distorted along the comparatively long flight 76, particularly with the aid of the rubber wales of the sleeve 21.

The interposition of the pulley 54 has the effect of causing the belt to move at a true right angle relationship to the work shaft 14. The distance between the take-off landing line 44 and the landing line 80 is so short that In short, the pressure exerted by the work tending to cause the belt to move to the right, in this instance, is

overcome bythe slope of the pulley which seems to give the right edge of the belt a slight redirection in the opposite direction.

Attention is invited to the wrinkle 82, see Figure 3. This wrinkle is slightly exaggerated. The inner edge 84 of the pulley 54 is beveled so as not to cut the under side of the belt. There is a pull by the balance of the belt, indicated by the numeral 86, see Figures 3 and 5, to the left. This pull opposes the pulley which moves the belt out of the approach flight path 52, see Figure 2. This wrinkle spreads into a sort of: valley indicated by the numeral 88 in Figure 5.

No adverse efiect is noticed when paper-backed sandpaper is used. However, the thin textile-backed paper develops a permanent wrinkle along the dotted line 90 in Figure 5, and this leads to the belief that the foregoing explanation is sound. It suggests that the sandpaper or sand textile outside .the strake 26, and referring to Figure Land bearing general number 86, resists stretching and tends to pull the strake 41 to the left. This in conjunction with a re-direction of the edge 40 of the pulley probably accounts for the success of the arrangement. There is no fraying of the edge of the paper and the distortion at any point is not sufiicient to damage the seam 28.

Returning to Figure l, applicant has a similar pulley 92 in reverse position, on the left-hand edge of the belt.

In operation, the device functions admirably. A workman may insert a workpiece such as 38 at any point, transversely of the belt. This is important from the standpoint of speed of operation. For example, in running fourto six-inch wide skees through the machine, the workman may feed them one beside the other as fast as he can pass them in. It is self-evident that the belt goes from no load to maximum load almost instantly or from no load to a selected partial load. The transverse thrust placed upon the belt varies greatly. The belt moves up on one pulley and stops. A moment later, it may move across the roll up onto the opposite pulley. The operators are able to put a maximum pressure on the feed roll shaft 30 so as to effect a maximum cut.

While the device has been described in connection with a sanding machine for wood, the machine shown is also used for polishing metal. The tendency to creep is less, but the pulleys function just as effectively.

Having thus described his invention, what applicant claims is:

1. A machine for surfacing articles comprising a frame, two substantially parallel spaced rolls mounted on said frame, a belt having an outer abrasive surface entrained over said rolls, and means mounted on the frame engageable with a flight of said belt and responsive to lateral creeping thereof for pressing a surface against the underside of a comparatively broad strake of the belt adjacent either edge thereof.

2. The machine of claim 1 wherein the means for pressing outwardly the belt is positioned close to the roll toward which the belt is moving.

3. The machine of claim 1 wherein the means for pressing the belt outwardly has a shoulder inwardly of the edge of the belt and the means is moved outwardly sufficiently far so as to create. a valley in the belt sloping toward the longitudinal center of the belt.

4. A machine for surfacing articles comprising a frame,

two substantially parallel spaced rolls mounted on said frame, a belt having an outer abrasive surface entrained over said rolls, a shaft positioned at right angles to the axis of one roll and parallel to the plane containing the axes of both rolls, and an arm pivotally mounted on said shaft, said arm including a surface intercepting the laterally projected inner surface of the approach flight of the belt at an obtuse angle, whereby when the belt creeps laterally it increasingly engages said surface until it pivots the arm so as to push outwardly a comparatively broad strake of the belt adjacent an edge thereof.

5. Amachine forsurfacing articles comprising a frame,

two substantially parallel spaced rolls mounted on said frame, a belt having an outer abrasive surface entrained over said rolls, a shaft positioned at right angles to the axis of one roll and parallel to the plane containing the axes of both rolls, an arm pivotally mounted on said shaft, an elongated cylindrical pulley rotatably mounted on the arm so that a line on its surface parallel to its axis intercepts the laterally projected inner surface of the approach flight of the belt at an obtuse angle, whereby as the belt creeps laterally, it increasingly engages the surface of the pulley until it pivots the arm 50 as to push outwardly a comparatively broad strake of the belt adjacent an edge thereof. 

